A Short History of Pyrite
and Acid Rock Drainage:
An Engineer’s Perspective of ARD
By Jim Gusek, P.E., Sovereign Consulting Inc.
Golden, Colorado
 Pyrite history, mineralogy & microbiology
 Testing procedures
 ARD Tetrahedron review
 Best Management Practices overview
 Engineering considerations
Acid Rock Drainage
IN PERPETUITY
Unless we can find practical
source control remedies
A Little History and Background…
• Pyrite’s name comes from the Greek, pyrites lithos, “the
stone which strikes fire”
• Iron sulfide (FeS2) – “fool’s gold”
• The crystals form in the Isometric System; cubes,
octahedrons, pyritohedrons and combinations of these and
other forms
• It also may be found in radiating disks, hair-like crystals,
concretions, and massive lumps in sulphide ore deposits
• Pyrite sometimes also contains small amounts of cobalt,
nickel, silver or gold as well as selenium (replaces sulfur)
• Other metals can replace the iron (e.g., copper) but then it’s
no longer pyrite…
• Most abundant of all sulfide minerals and occurs in all kinds
of rocks (sedimentary, metamorphic, igneous).
How and where does pyrite form?
Telethermal/biological (Sedimentary Environments)
• Organic deep ocean sediments (marine shale)
• Coal swamps (sulfate-reducing biochemical reactors too)
• Roll front uranium deposits
Epithermal/biological and abiotic (Igneous Environments)
• Hot springs
• Alteration zones near igneous intrusions
Mesothermal/Hypothermal / abiotic (Igneous &
Metamorphic Environments)
• Black smoker hydrothermal vents on seafloor
• Igneous intrusions
Common Pyrite Forms
• Framboidal
• Crystalline
~20 µm
Ref: GARD Guide
Mother Nature has been making pyrite for quite a while but
it’s only been recently in geologic time that it’s become a
problem…
Acid Rock Drainage Tetrahedron
Fuel
Water
FIRE
Air
Heat
ARD
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
Acid Base Accounting
Static Testing
•
•
•
•
Paste pH
Acid-Generation Potential
% Sulfur (pyritic & total sulfur)
Neutralization Potential
Acid Base Accounting
• Humidity Cells
• Column Tests
Tests rarely address potential remedies to ARD at a given site;
sure, they predict that ARD will be a problem but…
The results don’t provide me with any useful design data. This
needs to change…
Overview of Best Practice Methods
Early avoidance of ARD problems is a best practice
REF: GARD Guide 2010
www.gardguide.com
technique that may be achieved through integrating
results of characterization and prediction, described
in Chapters 4 and 5, along with mine planning,
design and waste management strategies.
Sources
Intervention
Vertical Pathway
Groundwater Perspective
Pathways
Measure
Performance
Receptors
ARD Mitigation Framework
Ref:
GARD
Guide
2010
Best Practice Methods (1)
• Avoidance
• Special handling methods
–
–
–
–
–
–
–
–
Incorporate into mine plan
Segregation
Tailings desulphurization
Compaction and conditioning
Encapsulation and layering
Blending
Co-disposal
Permafrost and Freezing
REF: GARD Guide 2010
What about
Abandoned
Mines?
Best Practice Methods (2)
• Dry Cover Methods
–
–
–
–
–
–
–
Soil
Alkaline
Organic
$ynthetics
Gas barriers
Vegetation
Landform design
Re-mining; backfilling; passivation; hydrodynamic controls
• Water Cover Methods
–
–
–
–
–
–
Subaqueous disposal
Partial water cover
Wetland covers
Attenuation
Stream flow regulation
Water recycle and reuse
REF: GARD Guide 2010
Best Practice Methods (3)
• Additions and Amendment
Methods
–
–
–
–
Passivation
Alkaline materials
Organics
Bactericides
???
Re-mining; backfilling; passivation; hydrodynamic controls
• Water Management Methods
– Hydrogeological & Hydrodynamic
Controls
– Dewatering
– Diversion
– Flooding
– Seals
How to implement at
abandoned mines?
Acid Rock Drainage Tetrahedron
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
DO NOTHING = PERPETUAL TREATMENT
DO SOMETHING (anything) = PATHWAY TO WALK-AWAY
Prevention/Source Control Summary
• Wet Encapsulation (submergence: adit
plugs/pit flooding) - keep air/oxygen
out
• Passivation additives (alkaline, organic,
other) change pyrite surface
chemistry
• Bactericides (sodium lauryl sulfate, etc.)
kill bugs & slow ARD kinetics x 10-6
• Dry Encapsulation (covers or caps) keep water out
Acid Rock Drainage Tetrahedron
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
Flooding Situations to Exclude Air
• Subaqueous tailings deposition
• Adit plugging - approach with
caution
• Pit flooding (upper benches might
be exposed – timing is everything)
Subaqueous Tailings Deposition
1 meter of no Fe+3 water cover
is sufficient to cut off oxygen to
disrupt ARD tetrahedron
Expect Problems with Flooding Underground Mines
Acid Rock Drainage Tetrahedron
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
Surface
“Passivation”
Passivation Additives (Liquid/Solid)
• Alkalinity (limestone, lime, cement
kiln dust, steel smelter slag)
• Organic Material (alcohol, sugars,
agricultural wastes, municipal
biosolids, waste milk [patented])
• Other (Phosphate, micro-encapsulation reagents (silicates), KMnO4 )
Passivation Additives - Cheap alkalinity
• Limestone (quarried) – crusher
fines?
• Dolomite
• Lime kiln or cement kiln dust
• Steel slag
• Sodium bicarbonate
Note: We need to consider the physics of delivering and
distributing a solid into a porous medium
Passivation Additives - Cheap organics
• Sawdust (the finer, the better)
• Paper (newsprint, office waste
[shredded])
• De-inking residue
• Biosolids
• Other?
Note: We need to consider the physics of delivering and
distributing a solid into a porous medium
Surface Passivation - Physical –Bio Coatings
• Keeco Mix (micro-silica)
• Potassium permanganate (Glen Miller, UNR)
• Milk (patent pending by Western Research
Institute); bacteria out-complete acido-thiobacillus
• Potassium humate (commercial agricultural
amendment)
• Others?
Note: We need to consider the physics of delivering and
distributing a coating into a porous medium
A Possible Solution:
Use FOAM as a delivery medium
Use waste milk as a portion of the liquid
 Use sodium lauryl sulfate or alkyl-benzene
sulfonate (bactericides) as part of the
surfactant mix
 Add powdered limestone for alkalinity
 Add paper, sawdust, or biosolids as the
organic Ref: Gusek, et al., ASMR 2012

This process is very similar to pressurized grouting, only the
grout mass is mostly gaseous, engineered to be temporary,
and designed to deposit a coating of active ingredients
Acid Rock Drainage Tetrahedron
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
Microbial
“Passivation”
Known Bactericides
• Sodium lauryl sulfate (SLS)
• Slow release commercial products
– ProMac (no longer available)
• Alkyl-benzene sulfonate (laundry
detergent is cheaper than SLS)
• Sodium Thiocyanate (NaSCN)
• Bi-Polar Lipids (patented)
Bactericides for Suppressing Acidithiobacillus Ferro Oxidans
• Temporary effect only? (maybe)
• Vaccination vs. medication? When do
you apply it?
• Case History - coal waste pile in PA
(Plocus & Rastogi, ASSMR, 1997)
• What else does it take to prevent
“re-infection”?
Encapsulation/Waste Management
• Segregation of acid-producing wastes (waste
rock or tailings) may be helpful in managing
wastes to minimize ARD formation
– protect waste from surface and ground
water (liner and cap systems) as needed
– if waste is “fresh”, consider underwater
disposal by flooding or submergence;
permanent flooding must be guaranteed
– What’s the pyrite “cut-off” grade that
triggers encapsulation?
Acid Rock Drainage Tetrahedron
Caps and
Covers
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
Cap/Cover Types
• Infiltration Barrier - most applicable in
wet climates – Default design
• Moisture Retention/Evapotranspiration
(store &release covers) - most applicable
in arid climates
• Organic Barrier - inexpensive source
material available (forestry waste,
agricultural waste, municipal biosolids,
BCR effluent?)
Infiltration Barrier Cap
Some Moisture
Storage
Moisture Retention/ET Cap
Moisture
Storage
You need to consider slope aspect! Shady and
sunny areas of the facility will have different ETs!
Organic Barrier Cap
Organic-Rich Solution
Some Moisture
Storage
OXYGEN
DEPLETION
MIXED
WASTE &
ORGANIC
ZONE
Design Assistance
Use EPA H.E.L.P. Model (or other
models) to evaluate cap physical
performance.
Hydrologic Evaluation of Landfill Performance
http://el.erdc.usace.army.mil/index.cfm
Under “models & tools”
Go to “landfill”
Other Water–Related ARD Mitigation Controls
• Pa$te Tailing$ Di$po$al
• Managed (Sub-Aerial) Tailings Deposition
• Wick Drains
• Co-Disposal of Tailings and Waste Rock
Paste Tailings Disposal - Store Solids, NOT Water
Plan View, Typical Sub-Aerial Tailings Basin
Header Pipeline
Slurry Offtake (typ)
Deposition Zones
Starter
Deposition
Embankment
Tailing Basin
Decant Pond
ZONE C
ZONE B
Return
Pipeline
ZONE A
Tailing Pipeline
Mill
Managed Tailings Deposition Stores Solids, NOT Water
Managed (Sub-Aerial) Tailings Deposition
Week 0 - depositing
Week 2 – ready for
another lift of tails
Rubber-tired equipment can drive on sub-aerial deposited
tailings within a week or two of cessation of placement
Sub-Aerial Tailings Deposition
SUPERNATANT
DRAINAGE
EVAPORATION
Surface
Cracking
Dense,
Impermeable,
Dry,
Ready-forcovering
STAGE 1
STAGE 2
STAGE 3
STAGE 4
WASTE SLURRY
IS DEPOSITED
IN A THIN LIFT
AFTER
SETTLING
AFTER DRAINAGE
[100% SATURATION]
AFTER DRYING
[PARTIAL
SATURATION]
East, et al., circa 1989
Wick Drains
Courtesy: Hayward Baker
Courtesy: Hayward Baker
~ 4 inches/
10 cm
• Physical method for releasing
excess
pore
pressure
• Borne in geotechnical stabilization of dredged
material to create dry land
Courtesy: Aerix Industries
• Commercially available
Permeable concrete “wick”
Co-Disposal of De-Watered Tailings and Waste Rock
Glacial till – natural analogue
Refs:
Wilson et al. ASMR/7th ICARD 2006 (St. Louis) &
Wilson et al. 6th ICARD 2003 (Cairns)
Co-Disposal of De-Watered Tailings and Waste Rock
www.tailingsinfo.com
Co-Disposal Alternative
• “Fluidize” paste or
dry tailings with
foam (not patented)
• Land-apply foamfluidized tailings on
top of lift of coarse
mine waste, (rip
waste if needed),
compact if needed.
3 to 5% moisture
content
Courtesy: Aerix Industries
Co-Disposal Alternative Design Opportunity
Summary of ARD Prevention Measures
Disrupt the ARD TETRAHEDRON by
using:
– Pyrite surface passivation amendments
– Bactericides (more passivation)
– Encapsulation (dry or wet)
Alone or in combination
Incorporate these concepts into the ENGINEERING
of the ARD management situation;
Testing should yield information to support an
engineered design basis.
Acid Rock Drainage Tetrahedron
Water
Oxidizer
(Air, Fe+3)
Bacteria
Pyrite
DO SOMETHING (anything) = PATHWAY TO WALK-AWAY
Thank You
“In France, a chemist named Pilatre de
Rozier tested the flammability of hydrogen
by gulping a mouthful and blowing across an
open flame, proving at a stroke that
hydrogen is indeed explosively combustible
and that eyebrows are not necessarily a
permanent feature of one's face.”
“There are three stages in scientific
discovery. First, people deny that it is true,
then they deny that it is important; finally,
they credit the wrong person.”
― Bill Bryson, A Short History of Nearly
Everything
jgusek@sovcon.com